27 Oct 1944USS Flounder (Cdr. J.E. Stevens) departed from Brisbane for her 4th war patrol. She was ordered to patrol in the South China Sea.

10 Nov 1944German U-boat U-537 was sunk in the Java Sea east of Soerabaja, in position 07°13'S, 115°17'E, by torpedoes from the US submarine USS Flounder (Cdr. J.E. Stevens).

21 Nov 1944USS Flounder (Cdr. J.E. Stevens) torpedoed and damaged the Japanese army cargo ship Gyosan Maru (5698 GRT) in the South China Sea in position 10°36'N, 115°08'E. The damaged Japanese ship is later finished off by USS Guavina.